1. Field of the Invention
The present invention relates generally to gas turbine engine axisymmetric vectorable nozzles and, more particularly, to a flap to seal retainer.
2. Discussion of the Background Art
One type of conventional gas turbine engine exhaust nozzle includes primary and secondary exhaust flaps arranged for defining a variable area converging-diverging exhaust nozzle. The exhaust nozzle is axisymmetric, or annular, and exhaust flow is confined by the primary and secondary flaps being positioned circumferentially adjacent to each other, respectively.
The secondary flaps, for example, have a forward end defining a throat of minimum flow area and an aft end having a larger flow area for defining a diverging nozzle extending downstream from the throat. The secondary flaps are variable, which means that the spacing between the secondary flaps as they are moved from a smaller radius position to a larger radius position must necessarily increase. Accordingly, conventional exhaust nozzle flap seals are suitably secured between adjacent ones of the secondary flaps to confine the exhaust flow and prevent leakage of exhaust flow between the secondary flaps.
An advanced axisymmetric vectoring nozzle (AVEN.TM. nozzle) has been developed and patented in U.S. Pat. No. 4,994,660, entitled "AXISYMMETRICAL VECTORING EXHAUST NOZZLE", by Hauer, assigned to the present assignee, and herein incorporated by reference. An axisymmetric vectoring nozzle provides a means for vectoring the thrust of an axisymmetric convergent/divergent nozzle by universally pivoting the divergent or secondary flaps of the nozzle in an asymmetric fashion or in other words pivoting the secondary flaps in radial and tangential directions with respect to the unvectored nozzle centerline.
Vectoring nozzles, and in particular axisymmetric vectoring nozzles of the type disclosed in the Hauer reference, provide positionable secondary flaps. These secondary flaps are positionable not only symmetrically, relative to a longitudinal centerline of the exhaust nozzle, but may also are positionable asymmetrically relative thereto for obtaining pitch and yaw vectoring. In such a vectored position, adjacent secondary flaps are positioned askew from each other, and therefore the exhaust nozzle flap seal disposed therebetween must be effective for maintaining sealing also as the secondary flaps are positioned for vectoring.
Furthermore, since the exhaust nozzle is channeling relatively hot combustor discharge gases, the exhaust nozzle flap seals must be able to accommodate such relatively hot temperatures and differential movement of structural elements due to differential heating and cooling thereof.
Retaining the flaps and adjacent seals in place for an axisymmetric nozzle is very difficult because of the varying degree of askewness between the flaps and seals encountered during asymmetric operation of the nozzle for thrust vectoring. The seal has to be retained radially, with respect to the nozzle's centerline, and circumferentially to prevent the flap seals from becoming unfeathered from the adjacent flaps. Radial retention between the seal and flap is required to counteract the inverse exhaust pressures that occur when there is higher pressure on the radially outer surfaces of the seal and flap than on the radially inner surfaces. Circumferential retention is required to prevent unfeathering between the divergent flap and seal which may occur during vectoring operation of the exhaust nozzle or in the case of an nozzle actuator hydraulic system (or other actuating system) failure.